With over 40 million people estimated to be infected with HIV-1 worldwide, there is a global urgency to develop a vaccine against the virus. Results from several studies suggest that it might be possible to prevent disease progression if a vaccine can elicit potent antiviral immunity that can control virus replication early during acute infection phase. Past studies have demonstrated that Gag-Pol-Env vaccine regimens based on recombinant live viral vector-prime followed by subunit protein-boost are quite effective against lentivirus challenges in macaques. The long-term objective of the projects being proposed is to improve the protective efficacy of existing vaccine candidates by incorporating recombinant parainfluenza virus (rPIV) vectors, which can elicit strong mucosal immunity, and by additionally targeting Nef, Tat and Rev, which are expressed early in infection cycle and play critical roles in HIV-1 replication and pathogenesis. The specific aims of the study are: (1) to generate and characterize biological properties of rPIVs expressing SIV/HIV-1 proteins, (2) to produce and purify subunit proteins that will be used as boosting antigens, and (3) to evaluate immunogenicity, synergistic potential and protective efficacy of rPIVs in small laboratory animals. Successful completion of these studies will provide the basis for future evaluation of protective efficacy against pathogenic SHIV in macaques, and would represent a major step forward in AIDS vaccine development efforts.